docs: def add_dup(self, pkt):
          """This method adds a dup for a packet to the metrics."""
          log.debug("Recording a dup of %s", pkt)
          s = str(pkt)
          if s in self.dups:
              self.dups[s] += 1
          else:
              self.dups[s] = 1
          tftpassert(self.dups[s] < MAX_DUPS, "Max duplicates reached")